1. Field of the Invention
The present invention relates to a means of testing the pressure integrity of tubulars, as commonly but not exclusively used in oil and gas wells to convey produced formation fluids from a subsurface producing formation to the surface. More particularly, the present invention relates to a means to internally test the pressure integrity of a tubing connection by forming an internal test chamber adjacent to the connection and pressuring the chamber to a desired test pressure. The test chamber is formed by inserting a generally cylindrical tester body having multiple spaced-apart external circumferential seal elements into the tubular, and positioned with at least one seal element above the connection and at least one seal element below the connection. A seal gas supply line supplies seal gas pressure to pistons on the tester body which move and expand the seal elements against the tubular wall, thereby creating a test chamber defined by the upper and lower seal elements, the tester tool body, and the tubular wall. Then, a test gas is introduced into the test chamber until a desired test pressure is achieved. A sensing means is employed on the exterior of the tubular adjacent to the internal test chamber to capture and detect any escape of test fluid from the tubular, showing a leak thereby.
More particularly, the invention relates to a means for maintaining the seal gas supply line at a desired pressure between tests to avoid lengthy re-pressuring of the relatively large line volume for each test, saving overall testing time. In addition, the apparatus provides a means for retaining and recycling a substantial part of the seal gas thereby greatly reducing the required volume and cost of the expensive gas. Further still, the invention provides a means to positively prevent excessive seal piston travel and resulting damage to the tester body seal elements.
2. Description of the Prior Art
Tubular piping of all types is commonly used in industrial applications to transfer fluids from one point to another. In particular in the oil and gas industry, tubular goods, commonly referred to as tubing strings, measuring many of thousands of feet in length are employed in oil and gas wells to convey produced fluids, namely oil and natural gas, from a subsurface producing formation to the surface. The tubing string runs within a larger diameter tubular known as casing which supports and seals the wellbore wall. Oil and gas are typically encountered at high pressures, and therefore pressure integrity of the tubing string is of utmost importance. Leaks in the tubing string, permitting oil and natural gas to escape from the tubing string into the tubing/casing annulus, create a highly dangerous situation with the possibility of pollution, loss of natural resources, and injury to personnel, since oil and gas are highly flammable.
The increasing scarcity of shallow, easily producible formations has driven the oil and gas industry toward progressively deeper producing intervals where much higher formation pressures are usually encountered. Also, as the more desirable formations with relatively non-corrosive formation fluids become scarcer, oil and natural gas are increasingly produced which contain various corrosive components, such as hydrogen sulfide. These corrosive fluids attack metals; while the tubing strings used in such situations may be internally coated to combat corrosion, or made of corrosion-resistant alloys, the casing string is often not corrosion resistant due to the high cost of such materials. The hostile producing environments of high pressure and corrosive fluids make pressure integrity of the tubing strings ever more important. In addition, tremendous capital expenditures are being made on oil and gas exploration and production ventures in offshore waters in water depths now measured in thousands of feet. The cost to install tubing strings in oil and gas wells in these water depths is extremely high, and it is of critical importance to test tubular strings so as to ensure the highest possible pressure integrity.
Ensuring pressure integrity of tubular connections comprises two primary actions: first, proper techniques to make up the (typically) threaded connections joining joints of tubing; and second, testing the connections after they are made up to verify that, at least at that time, the connections are truly pressure-tight.
Devices and methods to test the pressure integrity of tubular connections used in oil and gas wells have existed in various forms for some time. Testing methods generally comprise inserting an elongated tester body having multiple external circumferential seal elements into a tubular. The seal elements are then expanded against the inner wall of the tubular, forming a pressure seal. In this manner, a test chamber is created, defined by the inner tubular wall, upper and lower seal elements, and the tester body. A test fluid is introduced into this test chamber to achieve a desired test pressure. Any leaks in the connection are then determined by detecting escape of the test fluid. In earlier test apparatus, the test fluid was typically water, used primarily for cost and ease of leak detection with the relatively crude detection methods then available. Water being generally readily available, the cost is low. Earlier leak detection comprised monitoring the test for a pressure drop, and a leak in a water-filled chamber causes a relatively large and easily detectible pressure drop in the test chamber since water is relatively incompressible.
However, a disadvantage to using water as a test fluid lies in the integrity of the resulting test. Monitoring pressures to determine leaks with water reveals only relatively large leaks, and small leak paths that may not permit water to flow through, and thus not show up as a leak, may permit lower viscosity liquids (such as oil) or gas to flow through. Thus, a tubular connection which does not leak when tested with water may leak when other fluids are applied to it under pressure. Test integrity is highest when a gaseous test fluid is used, in particular one with a low molecular weight such as helium, since the test gas will leak through very small leak paths. Although gas testing yields the highest quality pressure test, gas testing is costly for two primary reasons: test time, largely due to the time to re-pressure the test and seal gas volumes between connection tests; and cost of the noble gas (such as helium) vented from the tool and lines upon depressurization, such gases being a relatively scarce and expensive natural resource.
Due to gas compressibility, leak detection by monitoring pressure in the test chamber is not a sufficiently accurate means to detect small leaks. For this reason, alternative means for detecting the escape of the test gas have been developed. Commonly, a noble gas such as helium is used as a test gas, which is readily detectable in very small concentrations by a mass spectrometer. A sleeve-type means is used to surround the exterior of the tubular adjacent the test chamber and to capture any escaped test gas, and then to sense the presence of any escaped test gas with a mass spectrometer.
Test integrity is best preserved by completely avoiding any liquid in the test apparatus, using gas for the seal fluid in addition to the test fluid. Although recycling of the test gas is generally not desirable due to possible contamination, it is desirable to recapture and recycle the seal gas, which comprises a relatively much larger volume. This could be done by completely bleeding off the pressure in the seal gas supply line and tester body and routing the bled-off gas to a reclamation tank. A disadvantage of that procedure is that the time used in re-pressuring the entire supply line (comprising most of the seal gas pressurized volume) and tester body to the desired seal pressure is quite lengthy, greatly increasing test time and associated costs; this is a key problem presented by prior art test tools.
Another problem exists with prior art test tools. The seal elements are typically doughnut-shaped elements of a resilient material, generally a rubber compound. In their relaxed condition, the maximum outer diameter of the elements is somewhat less than the inner diameter of the tubular. As the pistons on the tester body are forced against the seal elements by the seal gas pressure, the elements are squeezed and deform outward, forming a seal against the tubular wall. However, with current tools, there is no positive limit on the distance that the pistons can travel; that is, if excessive seal gas pressure is applied, the pistons will move too far and will damage the seal elements, requiring repair of the tool with the resulting lost time cost. The present invention solves this problem. The pistons have an extended neck which extends through the central hole in the seals into an annular cavity formed by the body of the tool and retaining flanges on the tool. The length of the piston neck and cavity positively limits the distance that the pistons can travel, regardless of the applied pressure, and thus excessive deformation of the seals is prevented.
Loomis, U.S. Pat. No. 2,731,827 (Jan. 24, 1956); Loomis, U.S. Pat. No. 2,841,007 (Jul. 1, 1958); Loomis, U.S. Pat. No. 3,038,542 (Jun. 12, 1962); Loomis, U.S. Pat. No. 3,154,940 (Nov. 3, 1964); and Loomis, U.S. Pat. No. 3,165,918 (Jan. 19, 1965) all disclose conventional tubular connection testers without means of retaining seal fluid line pressure, and without means of preventing seal piston overtravel. Loomis, U.S. Pat. No. 3,165,919 (Jan. 19, 1965), and Loomis, U.S. Pat. No. 3,165,920 (Jan. 19, 1965), show separate seal and test fluid lines, but with pressure controls only remote from the tester body, and without the ability to retain seal line pressure between tests; further, seal piston overtravel is not prevented. Loomis, U.S. Pat. No. 3,199,598 (Aug. 10, 1965) teaches an apparatus for testing and repairing well pipes without means to retain seal fluid pressure. Pate, U.S. Pat. No. 4,852,393 (Aug. 1, 1989) discloses a pipe tube pressure tester.
None of these patents disclose the present invention. The prior art does not solve the time and related cost problems associated with gas pressure testing of tubular connections, and does not solve the problem of excessive piston travel and resulting seal damage from intentional or accidental excessive seal pressure. The prior art does not disclose an apparatus for testing the pressure integrity of tubulars with gas which:
.circle-solid. retains and recycles a substantial part of the seal gas so as to reduce gas costs; PA1 .circle-solid. maintains the seal gas supply line in a pressurized state between tests, thereby reducing test cycle time; and PA1 .circle-solid. positively limits travel of the tester body pistons regardless of the seal pressure applied to the pistons, thereby preventing damage to the seal elements caused by excessive piston travel.
This invention permits the testing operator to optimize the cost balance between the time saved between tests (increased time savings with a higher retained seal gas supply line pressure) and the volume of seal gas vented (increased volume savings with a lower retained seal gas supply line pressure).